Instructional media and technology : a guide to accountable learning systems / Phillip J. Sleeman, Ted C. Cobun, D. M. Rockwell. Sleeman, Phillip J. Cobun, Ted C., joint author. Rockwell, D. M., joint author. Educational technology. LB1028.3 .S57 371.3078 SLI Includes bibliographies and index. New York : Longman, c1979. c1979. 1979 Text viii, 374 p. : eng